Processes of this kind have been found to be especially suited to the dyeing of travelling carpet webs and are so exemplified in U.S. Pat. Nos. 2,218,811, 3,393,411, and 4,033,154, in United Kingdom Pat. No. 1,202,345, and in the present applicant's co-pending patent application Ser. No. 042,501. In these prior arrangements, each dye application station comprises a multiplicity of individual nozzles each giving rise to a discrete stream directed towards the passing carpet. The streams are typically computer controlled so that the portions of dye applied by the succession of stations are complementary and thereby give rise to a predetermined pattern. It will be appreciated that an accurately resolved pattern will be obtained, and maintained, only if there is a precise and on-going synchronism between the carpet movement and the dye applications. Synchronization is required longitudinally between the respective dye applications and laterally between the positions of the carpet and the nozzles at each application station.
Approximate longitudinal synchronism is achieved by clocking pattern application with respect to carpet speed and thereby retarding dye application at each station relative to dye applications at each preceding station to match the time taken for a carpet increment to travel between the stations. However, it is found that the precise delay time is dependent not solely upon carpet speed but more finely upon the relative dye pressures at the application stations, which in turn are determined, inter alia, by dye viscosity and by the proportion of nozzles simultaneously applying dye. At the commencement of a print run, these variables will be determined by the actual dye chosen, by atmospheric conditions and by the nature of the pattern to be produced.
At present, fine synchronization to correct for dye pressure variations is carried out by manual adjustment of the retard time for each station on the basis of experienced operator observation, which is time consuming and entails not insignificant carpet wastage, especially where pattern changeover is carried out with continuously moving carpet. Moreover, on a longer run, fine asynchronism may arise when, for example, ambient temperature changes affect dye pressures differently.